The situation in Haiti is "truly heart wrenching" in a nation that is "no stranger to hardship and suffering," President Obama said at a press conference Wednesday. He promised a "swift, coordinated and aggressive" effort including rescue workers and humanitarian aid as part of a coordinated international response.

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In Geneva, a spokesman for the International Committee of the Red Cross (ICRC) estimated that as many as 3 million people in the impoverished country may have been affected by the quake, according to the Associated Press. The ICRC predicted that it would take 24 to 48 hours for a clear picture to emerge of the scale of the destruction.

According to the UN, the island is the scene of widespread devestation. Collapsed buildings include the national penitentiary, where prisoners have escaped, the National Palace (President Rene Garcia Preval is said to be safe), the Parliament Building, the National Cathedral and at least four other ministry buildings including the finance ministry.

The main airport's control tower is said to have collapsed, hindering rescue efforts. But the airport is said to be operational, and planes carrying aid from the UN are expected to arrive in Port-au-Prince this morning. A UN spokesperson in Geneva says the road from the airport is badly damaged.

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The Tuesday afternoon quake had a magnitude of 7.0, according to the U.S. Geological Survey, and was centered just 10 miles from Port-au-Prince.

The center was also relatively shallow, less than 10 miles below ground, raising the risk of damage.

Karel Zelenka, a Catholic Relief Services representative in Port-au-Prince, told U.S. colleagues before phone service failed that "there must be thousands of people dead," a spokeswoman for the aid group told The Associated Press.

"He reported that it was just total disaster and chaos, that there were clouds of dust surrounding Port-au-Prince," Sara Fajardo said from the group's offices in Maryland.

State Department Asst. Secretary for Public Affairs P.J. Crowley told reporters that embassy staff "reported structures down. They reported a lot of walls down. They did see a number of bodies in the street and on the sidewalk that had been hit by debris. So clearly, there's going to be serious loss of life in this."

The United Nations confirmed that the building housing the UN headquarters in Haiti has collapsed. Up to 100 people are believed to be trapped in the rubble,10 have been brought out alive, and five people were confirmed dead at the site. According to a UN spokesman this morning, up to 150 UN personnel were in the building when the quake struck.

Early reports said a hospital in nearby Petionville had collapsed, and a videographer for The Associated Press said he could hear people screaming for help.

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"I've been here 34 years as a missionary, I've seen hurricanes, I've gone through sicknesses ?but I could never, ever imagine something like this," said Joel Trimble. "It felt like everything is shifting, nothing is sure underneath you."